Independence, Impartiality and Lack of Bias of Expert Witnesses

This page was last substantively updated or reviewed January 2021. (Rev. # 95818)

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General Principles

A qualified expert witness has a duty to the court to be "fair, objective and non-partisan." This duty "overrides" any obligation that they may have to the party calling them. An expert unable or unwilling to fulfill this duty "is not qualified to give expert evidence" and should not be allowed to do so. The duty arises out of the obligations for the expert to be impartial, independent, and without bias.

Independence is a factor in the fourth part of the Mohan test when balancing risks against the benefit of the evidence.

The Three Components of the Duty to the Court The expert's duty to the court requires that they be "impartial, independent, and without bias". This means the following:

1. impartial: they must provide an objective assessment of the relevant issues;
2. independent: their expert opinions must be the product of their own judgment, uninfluenced by the party who has retained them or the outcome of the litigation; and
3. unbias: experts must not unfairly favour the position of one party over the other.

Standard

The appropriate standard of a qualified expert is one that "would not change regardless of which party retained him or her."

Whether an expert should be allowed to give opinion evidence even where an interest or connection to the case exists is a "matter of fact and degree."

Effect of Failing to Meet the Standard

The lack of impartiality or ability to fulfill their primary duty to the court should render their opinion evidence inadmissible due to lack of impartiality or independence.

Role of Trial Judge as Gatekeeper

The trial judge must consider this duty at the "gatekeeper" stage of admission and may affect admission and weight.

Procedure

In certain circumstances, a voir dire has been required to test the alleged lack of independence against the opinion evidence, in particular the assumptions, known facts, and the level of expertise. But it should not be "advocacy dressed up as expert opinion."

Qualities of an Independent Witness

Qualities of an independent witness should include:

• expert opinion should be and should be seen to be the independent product of the expert uninfluenced as to form or content by the exigencies of litigation;
• the expert witness should provide independent assistance to the Court by way of objective unbiased opinion in relation to matters within his expertise. The expert witness should never assume the role of advocate.
• An expert witness should state the facts or assumptions on which his opinion is based. He should not omit to consider material facts which detract from his concluded opinion
• An expert witness should make it clear when a particular question or issue falls outside his expertise.
• If an expert's opinion is not properly researched because he considers that insufficient data is available then this must be stated with an indication that the opinion is no more than a provisional one
• If after the exchange of reports, an expert witness changes his view on a material matter ... such change of view should be communicated ... to the other side without delay and when appropriate to the Court.
• Where expert evidence refers to photographs, plans, calculations ... survey reports or other similar documents [these] must be provided to the opposite party at the same time as the exchange of reports

Burden of Proof

There is no presumption of independence or impartiality of a witness.

Particularly where there is no challenge to qualification the expert should attest in their evidence to "recognizing and accepting the duty" of independence, impartiality and absence of bias to pass the Mohan threshold.

"Realistic Concern" test

The burden is upon the party challenging qualification on the basis of bias to prove that there is a "realistic concern" that the witness is unwilling or unable to comply with the duty to provide "fair, non-partisan, and objective assistance."

Should the opposing party establish a "realistic concern", then the party calling the expert must establish on a balance of probabilities that the proposed expert is "able and willing to comply with their duty."

Law Prior to White Burgess

A lack of independence had traditionally not been a prerequisite to admissibility. Rather partiality usually goes to weight Some degree of favouritism is expected. Where the expert evidence is not independent, the weight should correspond to "the degree to which their opinions are supported or contradicted by other evidence and common sense". With "little or no support" the evidence could be rejected.

The appearance of bias alone on the part of an expert can render his opinion evidence inadmissible.

There is the suggestion that the expert's opinion may be inadmissible where the lack of independence creates enough prejudice to warrant exclusion.

Independence

Police-employed Experts

For police officer experts there is a "heightened concern" with respect to the impartiality of police expert witnesses.

Evidence Outside of Expertise Undermines Independence

Impartiality requires that the expert stay within the limits of their expertise and qualify their statements. When stating opinion they should be clear to distinguish their own professional opinion from "more generally accepted scientific knowledge" when they diverge.

Bias

Experts will rarely be excluded on the grounds of bias as it is a high threshold. There must be a "clear unwillingness or inability to provide the court with fair, objective and non-partisan evidence." Any lesser forms of bias will go to weight.

Bias comes in many forms, some of which may include:

• lack of independence (because of a connection to the party calling the expert);
• “adversarial” or “selection” bias (where the witness has been selected to fit the needs of the litigant);
• “association bias” (the natural bias to do something serviceable for those who employ or remunerate you);
• professional credibility bias (where an expert has a professional interest in maintaining their own credibility after having taken a position);
• “noble cause distortion” (the belief that a particular outcome is the right one to achieve); and,
• “confirmation bias” (the phenomenon that when a person is attracted to a particular outcome, there is a tendency to search for evidence that supports the desired conclusion or to interpret the evidence in a way that supports it).

There can be bias through reliance on research papers that "conform with the policy positions, normative views, and pre-conceived notions of the researcher."

Confirmation bias was identified as a major problem by the Goudge Report wherein the pathologists and coroners exercised a "think dirty" policy where their work was motivated by "the noble cause of redressing the long history of inaction in protecting abused children" and to “help ferret it out and address it.”

Examples

A retired police officer, experienced and training in investigating organized biker gangs is acceptable evidence. A proposed defence expert cannot be recruited to perform a cross-examination of a crown expert as it would place the expert in a position of advocate.

An experienced medical expert believed they had a duty only to the Crown and would refuse work as a "hired gun" for defence counsel.

Impartiality

Courts are often concerned with impartiality where the expert was involved in the application for a search warrant or the laying of charges.

An expert report that was "repetitious and argumentative" or "read like the appellant’s counsel’s written argument" will be signs of bias.

Best Practices

Practice

An expert in any type of litigation has duties and responsibilities that include:

1. Expert evidence presented to the court should be, and should be seen to be, the independent product of the expert uninfluenced as to form or content by the exigencies of litigation.
2. An expert witness should provide independent assistance to the court by way of objective unbiased opinion in relation to matters within his [or her] expertise. An expert witness . . . should never assume the role of an advocate.
3. An expert witness should state the facts or assumptions upon which his [or her] opinion is based. He [or she] should not omit to consider material facts which could detract from his [or her] concluded opinion.
4. An expert witness should make it clear when a particular question or issue falls outside his [or her] expertise.
5. If an expert's opinion is not properly researched because he [or she] considers [there to be] insufficient data . . . available, then this must be stated with an indication that the opinion is no more than a provisional one. In cases where an expert witness, who has prepared a report could not assert that the report contained the truth, the whole truth and nothing but the truth without some qualification, that qualification should be stated in the report

The expert's right to give opinion evidence imports an obligation of maintaining an attitude of "strict independence and impartiality."

It has been recommended that an "evidence-based approach" be taken to evaluate experts. This suggests four requirements:

1. the theory or technique utilized by the expert must be reliable, and used in a manner that is reliable;
2. the expert must keep an open mind to a "broad menu of possibilities" (not be biased);
3. the expert must be objective and comprehensive in collecting evidence -- including rejecting information not germane and transparent about the information and influences involved; and
4. the expert must proffer more than the mere opinion, including the complete reasoning process, shortcomings and fair guidance on the confidence in the opinion.

Best Practice example - Required Practice in Ontario Civil Bar

In the civil context, practice in certain provinces such as Ontario have required experts to acknowledge certain duties relating to their opinion. It is expected that they acknowledge their duties:

1. to provide opinion evidence that is fair, objective and non-partisan;
2. to provide opinion evidence that is related only to matters that are within the expert’s area of expertise; and
3. to provide such additional assistance as the court may reasonably require to determine a matter in issue.

They are further expected to acknowledge that these duties will prevail over any obligation owed to the party calling them as a witness.

Their reports are expected to contain the following:

1. The expert’s name, address and area of expertise.
2. The expert’s qualifications and employment and educational experiences in his or her area of expertise.
3. The instructions provided to the expert in relation to the proceeding.
4. The nature of the opinion being sought and each issue in the proceeding to which the opinion relates.
5. The expert’s opinion respecting each issue and, where there is a range of opinions given, a summary of the range and the reasons for the expert’s own opinion within that range.
6. The expert’s reasons for his or her opinion, including,
   1. a description of the factual assumptions on which the opinion is based,
   2. a description of any research conducted by the expert that led him or her to form the opinion, and
   3. a list of every document, if any, relied on by the expert in forming the opinion.
7. An acknowledgement of expert’s duty signed by the expert.